Various types of skin aging are caused by diverse factors, such as an increase in age, sunlight (ultraviolet radiation) exposure, eating habits, stress, etc. Examples of skin aging include pigmentation that produces blemishes, freckles, chloasmata, etc.; skin dullness; dryness; and wrinkles. Prevention of such skin aging is a great health and aesthetic concern, particularly for women.
Cosmetics containing purine substances were developed as a solution for skin aging. Purine substances are known for their wide-ranging effects, including the suppression of skin pigmentation and the retardation of skin aging. Examples of purine substances include adenine, adenosine, and adenosine phosphate. Examples of compositions for external use containing such purine substances include an 0/W emulsion composition containing adenine, etc., (refer to Patent Document 1) and a solid composition formed of an oil-in-water emulsion (refer to Patent Document 2).
Purine substances are phosphorylated in a cell and converted into ATP, which serves as an energy source. When applied to a problem skin area, a composition containing purine substances is percutaneously absorbed, and promotes ATP generation in the cell. The increase in the intracellular ATP level activates the metabolism of skin cells, promotes the cell cycle, and thereby facilitates skin turnover. The facilitation of skin turnover encourages the discharge of old horny cell layers and the provision of new horny cell layers. This stabilizes the water retentivity of the skin and makes the skin softer and more resilient, thereby making the skin smoother and reducing dullness.
However, with the recent trend toward more diverse and advanced physiological effects in external use compositions, there has been a demand for the development of an external use composition that more efficiently utilizes the advantageous effects of the purine substances.    Patent Document 1: Japanese Unexamined Patent 2002-234830    Patent Document 2: Japanese Unexamined Patent 2006-182746